Apparatus for inverting and returning sheets from a printer for large-sized paper

ABSTRACT

An apparatus for inverting and returning sheets from a printer ( 1 ) for large-sized paper comprises an inlet area ( 11 ) where the sheet is received from the printer ( 1 ), and an outlet area ( 12 ) where said sheet is returned to the printer ( 1 ). The apparatus comprises a frame ( 16 ) mountable on the support of the printer ( 1 ), and a guiding slit ( 18 ) in the inlet area, said guiding slit being defined by an upper wall ( 13 ) and a lower wall ( 17 ), where the lower wall ( 17 ) extends from the inlet ( 11 ) to a clamping slit ( 22 ) between a first pair of roller means ( 23, 24 ) for receiving and temporarily retaining the front edge of a sheet when seen in the advancing direction, said sheet being received through the inlet area. The lower guiding wall ( 17 ) is tiltable and adapted to be moved about a substantially horizontal axis from a sheet-supporting position to a downward sheet-releasing position. The frame ( 16 ) carries furthermore a second pair of roller means ( 33, 24 ) adapted to received the sheet from the first pair of roller means ( 23, 24 ) and to guide the sheet through the outlet area ( 12 ) and back to the printer ( 1 ).

TECHNICAL FIELD

[0001] The invention relates to an apparatus for inverting and returningsheets from a printer for large-sized paper, said apparatus comprisingan inlet area where the sheet is received from the printer, and anoutlet area where said sheet is returned to the printer, a front edge ofthe sheets remaining in front during the receiving, inverting andreturning movement of said sheets.

BACKGROUND ART

[0002] Various printers for large-sized paper are known, such as forinstance the HP Designjet 1050C/1055CM. Such printers are primarily usedfor simplex printing, viz. printing on one side of the paper, and theyare often used for the production of samples of for instance postersbefore the final printing is initiated. The paper is available in formof separate sheets fed manually into the printer from the front side ofsaid printer, or it is available in form of rolls fed into the printerthrough a suitable inlet and cut off therein in the desired length, saidlength being variable according to desire. After the printing procedure,the paper usually falls into a tray or basket arranged below theprinter, said tray or basket being secured to the support of theprinter.

[0003] Sometimes duplex printing is required, viz. printing on bothsides of the paper, and then it is necessary to invert the paper, which,of course, can be carried out manually, but various possibilities ofautomating said inverting procedure apply as well. Some printersallowing such a duplex printing comprise two printer sections forinitiating the printing on each side of the paper. Other printerscomprise a built-in sheet inverter integrated in the inlet area of theprinter with the result that it obstructs the passage of the sheet whensaid sheet is to be returned to the tray.

BRIEF DESCRIPTIONS OF THE INVENTION

[0004] The object of the invention is to provide an apparatus forinverting and returning sheets to a printer, where said apparatus ismounted independent of the printer and accordingly does not obstruct theusual operation of the printer during the printing on only one side, andwhere said apparatus furthermore can be mounted on an existing printer,such as a printer of the type described above, in a relatively easymanner.

[0005] The apparatus according to the invention comprises a framemountable on the support of the printer, and a guiding slit in the inletarea, said guiding slit being defined by a downward surface on an upperguiding wall and an upward surface on a lower guiding wall, where saidupward surface having a downwardly curving profile extends from theinlet area to a clamping slit between a first pair of roller means,whereby the lower guiding wall is tiltable and adapted to be moved abouta substantially horizontal axis from a sheet-supporting and -formingposition in which the guiding slit is formed and into a downwardlyextending sheet-releasing position, where in use the outlet area isplaced over and adjacent the inlet area, and where the frame carries asecond pair of roller means adapted to receive the sheet from the firstpair of roller means and to guide the sheet through the outlet area andback to the printer.

[0006] As a result the inverting of a sheet can be carried outcompletely outside the printer, and the resetting of the printer to aninverting of the sheet or to an ordinary use can be controlled merely bymoving the lower guiding wall between its two operational positionswhile it is simultaneously possible to move the entire sheet out of theprinter before it is returned to the printer again. The latter is inparticular achieved by the front edge of a sheet to be inverted beingadvanced to and retained in the clamping slit between the first pair ofroller means, whereafter the lower guiding wall is moved out of itssheet-supporting position and allows said sheet to be moved outwardsinto an increasing, downward loop in the area between the outlet of theprinter and the first pair of roller means until the rear end of saidsheet falls out and downwards into the area below the printer where abasket is preferably provided. Subsequently, the sheet is pulled upwardsand fed into the printer again by an activation of the roller means.

[0007] According to the invention it is particularly advantageous whenthe apparatus comprises an idler roll adapted to abut the top side of asheet between the inlet area and the first pair of roller means afterthe front edge of the sheet has been gripped by the first pair of rollermeans and the lower guiding wall has been tilted downwards into thedownwardly extending position, said idler roll being supported by thesheet and following said sheet in its downwardly curving free path assaid sheet leaves the printer. As a result it is ensured that the sheetdoes not form folds substantially longitudinal to said sheet when seenin the advancing direction thereof, especially due to various degrees ofmoisture applied during the printing when seen in the transversedirection of said sheet.

[0008] According to the invention the idler roll may be suspended in aspring means ensuring that the idler roll subjects the sheet to a forceweaker than the force originating from the weight of said idler roll,said spring means being connected to a driving means for retracting theidler roll into its uppermost starting position when the rear end of thesheet has passed the inlet area and has fallen down. In this manner itis avoided that the effect of the idler roll on the paper is restricted,and that said idler roll is easily returned to its starting position.

[0009] The two pairs of roller means may according to the inventionparticularly advantageously comprise a common roller and be driven bymeans of the roller means of the first pair of roller means co-actingtherewith, whereby a simple control of the operation of the roller meansis obtained.

[0010] According to the invention the apparatus comprises advantageouslya first sensor for detecting the arrival of the front edge of a sheetimmediately before said edge reaches the clamping slit between the firstpair of roller means, and for activating said first pair of roller meansso as to grip and advance said edge a short distance. As a result a highsecurity is obtained that the first pair of roller means achieves a goodgrip in the front end of the sheet before the lower guiding wall ismoved out of the sheet-supporting position.

[0011] Correspondingly the apparatus may according to the inventioncomprise a second sensor for detecting that the rear end of the sheethas left the printer. In this manner the returning of the above rollerto its uppermost position and the further returning of the sheet to theprinter are controlled in a simple manner.

[0012] Moreover, a measuring device may according to the invention beprovided in connection with the second pair of roller means forregistering the length of the sheet. As a result it is possible toefficiently monitor the operation of the apparatus despite a varyingresistance relative to the advancing of various lengths of sheets andweights of paper etc. in such a manner that it is always positivelyknown when the front end of the sheet has reached a specificpredetermined location in the printer during the advancing and when saidadvancing by means of the roller means is to be stopped.

[0013] Furthermore, the driving roller means may according to theinvention be provided with overrunning clutches so as to ensure that thesheet can be freely pulled forwards in the advancing direction when theadvancing device of the printer starts to advance the inverted sheet. Inthis manner it is avoided that the sheet is destroyed due to the effectof various advancing speeds.

[0014] Moreover a redirecting member may according to the invention beprovided at the guiding slit, said redirecting member being adapted todirect the front edge of a sheet downwards and into the guiding slit atthe arrival from the printer, whereby the paper is reliably fed intosaid guiding slit. The latter is of particular importance when the paperoriginates from a roll and accordingly has a tendency to bend upwards ina direction away from the guiding slit.

[0015] The redirecting member may according to the inventionparticularly advantageously comprise a Z-shaped sectional guide freelypivotally journalled about a horizontal axis above the outlet area,where the body of said Z-shaped sectional guide in the rest positionextends obliquely downwards and abuts by its lower end the edge of theupper guiding wall of the guiding slit adjacent the printer, andtogether with this guide rail it forms an acute angle facing the outletarea while the lower web of the sectional guide projects obliquelyupwards from the guiding wall towards the printer. According to its sizethe upper web ensures a good balancing of the sectional guide.

[0016] The frame may according to the invention be tiltably anddetachably mounted on the support of the printer in such a manner thatan easy access applies to the side facing the printer.

[0017] Finally, a further guide may according to the invention beprovided between the two pairs of roller means and the second pair ofroller means and the outlet area, respectively, in such a manner that anefficient guiding of the sheet during the advancing thereof is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is explained in greater detail below with referenceto the accompanying drawings, in which

[0019]FIG. 1 is a diagrammatic side view of a printer with an apparatusaccording to the invention, where parts have been removed for the sakeof clarity,

[0020]FIG. 2 illustrates on a larger scale a diagrammatic crosssectional view of parts of the apparatus according to the invention,

[0021]FIG. 3 is a side view of parts of the apparatus according to theinvention,

[0022]FIG. 4 illustrates parts of the apparatus seen from the oppositeside,

[0023]FIG. 5 illustrates on a larger scale the parts of FIG. 2, butwhere parts of the printer have been indicated and where the front edgeof a sheet or length of paper appears entering the guiding slit of theapparatus,

[0024]FIG. 6 corresponds to FIG. 5, but in a situation where the frontend of the sheet has reached a clamping slit between a first pair ofrollers,

[0025]FIG. 7 corresponds to FIG. 6, but where the front end of the sheetenters the clamping slit between the first pair of rollers,

[0026]FIG. 8 illustrates a subsequent situation, where asheet-supporting guiding wall has been moved downwards into a downwardlyextending sheet-releasing position,

[0027]FIG. 9 corresponds to FIG. 8, but where the sheet is about to forma downwardly curving fold while leaving the printer,

[0028]FIG. 10 corresponds to FIG. 9, but in a situation where the rearend of the sheet is cut off by means of a cutting device inside theprinter,

[0029]FIG. 11 illustrates a subsequent situation, where the sheet ishanging freely downwards inside the apparatus from the first pair ofrollers,

[0030]FIG. 12 corresponds to FIG. 11, but in an immediately subsequentsituation where the pair of rollers of the apparatus has been activatedand is about to return the sheet to the printer,

[0031]FIG. 13 corresponds to FIG. 12, but in a situation where the sheetenters the printer,

[0032]FIG. 14 corresponds to FIG. 13, but in a subsequent situationwhere the sheet has been returned completely to the printer and isleaving said printer while the rear side is being printed, and

[0033]FIG. 15 corresponds to FIG. 14, but in a subsequent situationwhere the sheet is moving downwards to a tray below the printer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034]FIG. 1 illustrates a printer designated the general referencenumeral 1 and comprising a support 2 with a base 3. An apparatusaccording to the invention for inverting a sheet of paper from theprinter is secured to the support 2 through a hinge connection with twoarms 4, 5. This apparatus is designated the general reference numeral 6.The printer is of a conventionally known type with a front provided withan oblong slit 7 opening on to the printer unit 8 which provides a sheetor a length 9 of paper with a print while it leaves the printer.

[0035] The printer comprises its own paper handling equipment in aconventionally known manner, said paper handling equipment being of aconventionally known type and accordingly not being illustrated anddescribed in greater detail. When the paper originates from a roll ofpaper, it is cut off after the printing in suitable, predeterminedlengths by means of a cutting device 10. Below the paper to be handledis throughout referred to as a sheet although in some situations it hasnot yet been cut off by means of the cutting device 10.

[0036] The printer in question is of such a type that it is intended forlarge-sized paper, i.e. paper widths of preferably 60 to 100 cm. Theapparatus 6 is arranged such relative to the slit 7 of the printer thatits opposing inlet area 11 and outlet area 12 are positioned oppositethe slit 7 of the printer. The inlet area 11 is defined by an upperstationary guiding wall 13 which is secured in a manner not described ingreater detail at each end to the end walls 14, cf. FIG. 4, and 15forming part of the frame 16 of the apparatus. This guiding wall 13extends from an area opposite the slit 7 of the printer and obliquelydownwards into the interior of the apparatus 6, and together with apivotal or tiltable lower guiding wall 17 it defines a guiding slit 18in the innermost area. This lower guiding wall 17 presents a curvedprofile in such a manner that in the state shown in FIG. 2 it curvesdownwards. At the inner end, the lower guiding wall is secured to ashaft 19 which is connected to the output shaft 21 of a motor 20 througha pulley drive on the outer side of the end wall 14 of the frame 16. Asa result the lower guiding wall 17 is adapted to be moved between theposition shown in FIG. 2 and the position inter alia shown in FIG. 8 inwhich it has been turned approximately 90°, and downwards into aposition in which it is suspended freely substantially verticallydownwards inside the apparatus 6. A clamping slit 22 is arranged betweentwo roller means 23, 24 opposite the end of the lower guiding wall 17adjacent the shaft 19. The first roller means 23 of these two rollermeans 23, 24 is a driving roller, and as illustrated in FIG. 3 thisroller 23 is connected to the output shaft 27 of a motor 26 through abelt drive on the outside of the end wall 15 of the frame 16. The shaft25 is connected to a pulley 28 through an overrunning clutch 29.

[0037] The roller means 23 comprises a plurality of rubber rings 30arranged at suitable intervals along the shaft 25. These rubber rings 30form the clamping slit 22 together with the second roller means 24. Thissecond roller means 24 comprises a plurality of cylindrical walls 31secured to a shaft 32, which in turn is freely pivotally journalled in amanner not described in greater detail, but such that it can be freelyturned by the driving first roller means 23. When seen in the useposition, a third roller means 33 is arranged at a level substantiallyvertically above the shaft 32 of the roller means 24. This third rollermeans 33 comprises a shaft 34, which is also free pivotally journalledin a manner not described in greater detail, but such that the secondroller means 24 causes the third roller means 33 to rotate because theyabut one another along their circumference.

[0038] A guiding profile 38 is mounted between the driving roller means23 and the third roller means 33, said guiding profile 38 comprising aninner side 39′ which extends coaxially about the axis of rotation of thesecond roller means 24 and at a short distance from the outer surface ofsaid roller means 24. Guiding webs 39 and 40 extend from this inner side39 of the guiding profile 38 and inwards between the rubber rings 30 onthe driving roller means 23 and the third roller means 33, respectively,also at a short distance relative to the outer side of the second rollermeans 24. Finally, a guide rail 41 is provided, which comprises asurface extending substantially tangentially to the outer side of thesecond roller means 24 and forwards to the outlet area 12 of theapparatus and in a direction towards the slit 7 of the printer.

[0039] A Z-shaped guide rail 42 is provided in the area opposite theoutlet area 12. At the ends this Z-shaped guide rail 42 is pivotallyjournalled on upwardly projecting brackets 43 secured to the upperguiding wall 13 which projects from the inlet area 11. The Z-shapedguide rail 42 is provided with an angular web at each end. These webs 44individually engage a shaft member 45 on the upwardly projectingbrackets 43 on the upper guiding wall 13. As illustrated inter alia inFIG. 2, the lower end of the Z-shaped guide rail 42 loosely abuts theend of the upper guiding wall 13 projecting towards the printer, whereasthe lower web 46 of said guide rail 42 projects obliquely upwards in adirection away from the apparatus. The upper web 47 of the Z-shapedguide rail 42 projects obliquely downwards and inwards towards theapparatus 6, and it has a balancing effect on the Z-shaped guide rail 42in such a manner that it can be turned counter-clockwise in a relativelyeasy manner when seen relative to FIG. 2, viz. out of the engagementwith the upper guiding wall 13.

[0040] A shaft 48 is arranged centrally above and at a short distancefrom the pivotally journalled guiding wall 17, cf. FIG. 2, said shaft 48comprising a freely pivotally journalled roller 49. At each end thisshaft 48 with roller 49 is suspended in a thin flat spring 50, which iswound in a helical manner about a cylinder 51 secured to a shaft 41. Asillustrated in FIG. 4, this shaft is driven by a motor 53 on the outerside of the end wall 14 of the frame 16. The motor 53 is a reversiblemotor and the shaft 52 is connected to the belt drive through anoverrunning clutch 54. The function of the roller 49 during theinverting process is described in greater detail below.

[0041] As indicated by means of a broken line in FIG. 2, a sensor 55, 56is arranged immediately in front of the clamping slit 22 between thedriving roller means 23 and the second roller means 24. These sensors55, 56 detect whether a sheet 9 has reached the clamping slit 22 bymeans of a light beam 57 passing between the rubber rings on the drivingroller means 23 and the third roller means 33 as well as a space in thecylindrical wall 31 on the second roller means 24.

[0042] When the apparatus 6 is mounted on the printer, the controlsystem of the apparatus is connected to the control system of theprinter in such a manner that the apparatus is set such that it is readyto initiate an inverting of a sheet when the user of the printeractivates said printer to initiate the duplex printing, viz. theprinting on both sides. Such a state appears from FIG. 2 and FIG. 5.

[0043] The use of the apparatus is now described with reference to FIGS.5 to 15 showing the steps of the inverting process. As illustrated inFIGS. 2 to 5, the lower wall 17 is in a position where a theoreticalline between its pivot shaft 19 and its opposite free end issubstantially horizontal when seen relative to the cross section. Belowthis position is referred to as the horizontal position of the guidingwall 17, whereas when said theoretical line extends substantiallyvertically downwards the position is referred to as the verticalposition of said guiding wall 17.

[0044] FIGS. 5 to 15 include only the reference numerals important forthe description of the respective situation.

[0045] When the printer 1 has been activated to print on both sides of asheet 9, said sheet 9 passes during the printing by means of the printerunit 8 by its front end 60 directly into the guiding slit 18 between thestationary upper guiding wall 13 and the lower tiltable guiding wall 17,cf. FIG. 5. During this passage and especially when the sheet originatesfrom a roll and accordingly has a tendency to bend upwards, the frontend 60 of the sheet hits the lower web 46 of the Z-shaped guide rail 42and is thereby guided downwards below the upper guiding wall 13 and intothe guiding slit 18. During the continued printing by means of theprinter unit 8, the sheet 9 gradually reaches and enters the positionshown in FIG. 6, in which the front edge 60 of the sheet 9 refracts thelight beam 57 between the sensors 55 and 56. As a result, the drivingroller means 23 and 24 are activated to drive the front end of the sheet9 into the clamping slit 22 between the driving roller means 23 and thesecond roller means 24, cf. FIG. 7. This advancing of the sheet is onlycarried out a short distance whereafter the activation of the rollermeans 23, 24 is interrupted again. The front end of the sheet 9 is thenreliably retained in the clamping slit 22. Now the lower guiding wall 17is moved downwards into its vertical position, cf. FIG. 8, in which itno longer supports the sheet 9 being subjected to a printing.

[0046] During the continued advancing of the sheet 9, said sheet 9gradually forms a downward curve in the free space below the upperguiding wall 13, cf. FIG. 9. While the lower guiding wall 17 is tilteddownwards into its vertical position, the motor 53 associated with theroller 49, cf. FIG. 4, is activated. As a result, the roller 49 is moveddownwards into contact with the sheet 9 by a force being a combinationof the weight of said roller and an oppositely acting force from the twohelically wound flat springs 50 in which said roller 49 is suspended.When the shaft 52 is caused to rotate by the motor 53 in the directionindicated by means of an arrow 61, the roller 49 is lowered until itenters contact with the sheet 9 as described above. When the motorrotates at a higher speed than the speed involving the formation of thedownward curve, the associated overrunning clutch 54 declutches theconnection with the motor. The combined force effect by the helicallywound flat springs on the roller 49 and the associated shaft 48 is lowerthan the force of the gravity on said roller 49 and the associated shaft48. Therefore the roller subjects the sheet 9 to a force, but this forceis lower than the force originating from the gravity alone. The effectof the roller 49 on the sheet implies that said sheet is maintains agood curved shaped without forming longitudinal folds although theproperties of the paper can be uneven due to a nonuniform distributionof moist areas resulting from the printing.

[0047] When the sheet 9 has been completely printed, it is cut off whenit originates from a roll of paper by means of the cutting device 10,cf. FIG. 10. Then the rear end of the sheet falls, cf. FIG. 11, whilethe front end is retained in the clamping slit 22. The rear end of thesheet 9 is optionally placed in a tray not shown below the printer 1.

[0048] The termination of the printing process activates the apparatus 6to initiate the returning of the sheet 9 to the printer after a suitableperiod of time from the front side through the slit 7. This activationimplies that the driving roller means 23, cf. FIG. 12, is caused torotate in the direction indicated by means of the arrows. The primaryfunction of the third roller means during this advancing of the sheet 9is to measure the current advancing length of the sheet 9, which iscarried out by means of a measuring device not shown which registers therevolutions of the third roller means 33. The measuring is carried outin order to take into account possible factors having an effect on theadvancing process, such as the weight of the paper, the length of thesheet 9 etc.

[0049] During the advance the sheet 9 is guided by the guiding profile38 and the associated webs 39 and 40 as well as the guide rail 41. Whenthe front end 60 of the sheet reaches the Z-shaped guide rail 42, saidguide rail is tilted, cf. FIG. 13, away from its abutment against theupper guiding wall 13. When the front edge 60 of the sheet reaches aspecific area in the slit 7 of the printer 1, the advancing mechanismsof the printer are activated, said advancing mechanisms including avacuum effect and a rotation of rollers. The printer 1 reacts in thesame manner as when a sheet is manually fed into the slit 7 from thefront of the printer. The arrival of the front edge 60 to this specificarea in the slit 7 of the printer 1 is registered by means of themeasuring device associated with the third roller means 33, saidmeasuring device measuring the length of the sheet 9 passing the rollermeans in question as described above. While the sheet 9 is pulled in adirection back to the printer 1, the rotation of the motor associatedwith the roller 49 is simultaneously initiated with the result that theroller is moved upwards and back to its starting position. Now theprinter continues to pull the sheet inwards until it registers thearrival of the rear end of said sheet, which subsequently is the frontend during the printing of the rear side of the returned sheet 9.

[0050] The sheet is subjected to a tension because it is affected byboth the advancing system of the printer during the feeding through theslit 7 and the roller means 23, 24 and 33, and in order to reduce thistension the overrunning clutch 29 associated with the driving roller 23allows the roller means to rotate freely in the advancing direction inconnection with said tension. In order to simultaneously allow areturning a short distance of the sheet during the feeding processbecause the advancing mechanism of the printer sometimes subjects saidsheet 9 to a returning movement during said feeding process, therotating direction of the motor 26 of the driving roller means 23 isreversed during the initial phase of the feeding of said sheet into theslit 7.

[0051] When the printer 1 has registered the arrival of the rear edge ofthe sheet 9, the printing of the rear side of said sheet 9 is initiatedby means of the printer unit 8, cf. FIG. 14, while said sheet 9 issimultaneously guided out of the printer again. As illustrated in FIG.14, the lower guiding wall 17 is maintained in the vertical positionduring the latter operation. As a result the front end of the sheet isnot gripped in the guiding slit 18 of the apparatus 6 like in FIG. 5,but instead it moves downwards towards the tray optionally arrangedtherebelow, cf. FIG. 15. When the printing of the rear side of the sheet9 has been terminated, and when the printer has again been activated tocarry out a duplex printing, the lower guiding wall 17 of the apparatus6 is returned to the horizontal position shown in FIGS. 2 and 5 with theresult that the entire apparatus 6 is ready for initiating anotherinverting of a sheet.

[0052] The invention has been described in connection with a preferredembodiment. Many modifications can be carried out without therebydeviating from the scope of the invention. Pneumatic pistons not showncan for instance be incorporated in the arms 4, 5 of the apparatus, saidpneumatic pistons allowing the apparatus to be tilted according todesire into a position in which an easy access is provided to the sidefacing the printer.

1. Apparatus for inverting and returning sheets (9) from a printer (1)for large-sized paper, said apparatus comprising an inlet area (11)where the sheet (9) is received from the printer (1), and an outlet area(12) where said sheet (9) is returned to the printer (1), a front edge(60) of the sheets (9) remaining in front during the receiving,inverting and returning movement of said sheets (9), characterised inthat the apparatus comprises a frame (16) mountable on the support (2)of the printer, and a guiding slit (18) in the inlet area (11), saidguiding slit (18) being defined by a downward surface on an upperguiding wall (13) and an upward surface on a lower guiding wall (17),where said upward surface having a downwardly curving profile extendsfrom the inlet area (11) to a clamping slit (22) between a first pair ofroller means (23, 24), whereby the lower guiding wall (17) is tiltableand adapted to be moved about a substantially horizontal axis from asheet-supporting and -forming position in which the guiding slit (18) isformed and into a downwardly extending sheet-releasing position, that inuse the outlet area (12) is placed over and adjacent the inlet area(11), and that the frame carries a second pair of roller means (33, 24)adapted to receive the sheet from the first pair of roller means (23,24) and to guide the sheet (9) through the outlet area (12) and back tothe printer (1).
 2. Apparatus as claimed in claim 1, characterised inthat it comprises an idler roll (49) adapted to abut the top side of thesheet (9) between the inlet area (11) and the first pair of roller means(23, 24) after the front edge (60) of the sheet has been gripped by thefirst pair of roller means (23, 24) and the lower guiding wall (17) hasbeen tilted downwards into the downwardly extending position, said idlerroll (49) being supported by the sheet (9) and following said sheet inits downwardly curving free path as said sheet leaves the printer (1).3. Apparatus as claimed in claim 1 or 2, characterised in that the idlerroll (49) is suspended in a spring means (50, 51, 52), which ensuresthat the idler roll (49) subjects the sheet (9) to a force which isweaker than the force originating from the weight of the idler roll(49), and that said spring means (50, 51, 52) is connected to a drivingmeans (53) for retracting the idler roll (49) into its uppermoststarting position when the rear end of the sheet (9) has passed throughthe inlet area (11) and has fallen down.
 4. Apparatus as claimed inclaim 1, 2 or 3, characterised in that the two pairs of roller means(23, 24, 33) comprise a common roller (24) and are driven by means ofthe roller means (23) co-acting therewith in the first pair of rollermeans (23, 24).
 5. Apparatus as claimed in claim 1, 2, 3 or 4,characterised in that it comprises a first sensor (55, 56) for detectingthe arrival of the front edge (60) of a sheet (9) immediately beforesaid edge reaches the clamping slit (22) between the first pair ofroller means (23, 24) and for activating the first pair of roller means(23, 24) so as to grip and advance said edge a short distance. 6.Apparatus as claimed in one or more of the claims 1 to 5, characterisedin that it comprises a second sensor for detecting that the rear end ofthe sheet (9) has left the printer (1).
 7. Apparatus as claimed in oneor more of the claims 1 to 6, characterised in that a measuring deviceis associated with the second pair of roller means (33, 24), saidmeasuring device registering the length of the sheet.
 8. Apparatus asclaimed in one or more of the claims 1 to 7, characterised in that theroller means (23, 24, 33) are provided with overrunning clutches so asto ensure that the sheet can be pulled freely forwards in the advancingdirection when the advancing device of the printer (1) starts to advancethe inverted sheet (9).
 9. Apparatus as claimed in one or more of theclaims 1 to 8, characterised in that a redirecting member (42) isprovided for directing the front edge of a sheet at the guiding slit(18) in a direction downwards and into said guiding slit (18) at thearrival from the printer (1).
 10. Apparatus as claimed in claim 9,characterised in that the redirecting member (42) comprises a Z-shapedsectional guide freely pivotally journalled about a horizontal axisabove the outlet area (12), where the body of said Z-shaped sectionalguide in the rest position extends obliquely downwards and abuts by itslower end the edge of the upper guiding wall (13) of the guiding slit(18) adjacent the printer (1), and together with this guiding wall (13)it forms an acute angle facing the outlet area (12) while the lower web(46) of the sectional guide projects obliquely upwards from the guidingwall (13) towards the printer (1).
 11. Apparatus as claimed in one ormore of the claims 1 to 10, characterised in that the frame (16) istiltably and detachably mounted on the support (2) of the printer (1).12. Apparatus as claimed in one or more of the claims 1 to 11,characterised in that an additional guide (38, 41) is provided betweenthe two pairs of roller means (23, 24, 33) and the second pair of rollermeans (24, 33) and the outlet area (12), respectively.